External secretions are discharges that are discharged directly from the exocrine glandular cells or through the excretory ducts or the like onto the body surface or into a lumen. Tear and saliva are the typical external secretions and secretions from the nasal or the respiratory tract mucosa, secretions from the stomach or the intestine, discharges from the vagina, perspiration, etc are also included. Conditions resulting from external secretion disorders include dryness of various parts of the body such as “dry-eye syndrome” (xerophthalmia), “dry-mouth syndrome” (xerostomia), “dry nose syndrome” (xeromycteria), “dry-skin syndrome” (xeroderma), and “dry-vagina syndrome” (symptom of vaginal dryness); and chronic pancreatitis, chronic gastritis, and chronic bronchitis due to depression of the external secretion.
“Sjögren's syndrome”, an autoimmune disease, is one of the variety of known and unknown etiologic factors which may responsible for external secretion disorders. Sjögren's syndrome is characterized by dryness condition due to infiltration of inflammatory cells into the acinus of the exocrine gland and around the excretory duct, which results in destruction and atrophy of the acinus and the epithelial cells of the duct. Typical symptoms include eye and mouth dryness, as well as dryness of skin, nose, throat, bronchia, vulva, and vagina. For example, dryness of the respiratory tract may induce infections in the lung and sometimes may cause serious disorders such as pneumonia that may lead to death. The other major etiology is aging. Although the external secretion disorders may cause serious diseases as mentioned above, merely symptomatic treatment methods such as artificial hydration have been available for the disorders so far. Therefore, development of a fundamental treatment to improve the depressed external secretion has been desired.
One of the diseases caused by the external secretion disorders, and which has been a current keen interest in the medical and pharmaceutical field, is hypolacrimation including dry-eye syndrome.
Dry-eye syndrome is defined as a condition with decrease or change in quality of tear irrespective of the presence or absence of corneal and conjunctival lesion (Yamada et al., GANKI 43, 1289-1293(1992)). It include dry-eye conditions found in the patients of hypolacrimation, alacrima, xerophthalmia, Sjögren's syndrome, keratoconjunctivitis sicca, Stevens-Johnson syndrome, ocular pemphigoid, blepharitis marginal, and diabetes, etc.; post-cataract surgery dry eye; allergic conjunctivitis-associated dry eye; and age-related dry-eye syndrome. Further, dry-eye also includes the conditions found in hypolacrimation patients induced by long time visual display terminal (VDT) operations, room dryness due to air-conditioning and the like.
There are various etiologies of the dry-eye syndrome, including the above described and that have unidentified. However, at present, only palliative treatments for the dry-eye syndrome including administering an artificial tear solution to increase the quantity of tear retained within the conjunctival sac thereby relieve the subjective symptoms or protecting the eyes from dryness have been available. It has been desired to provide compositions which is capable of bringing satisfactory treatment, including improvement of hypolacrimation.
The tear secretion is classified into basal tear secretion and reflex tear secretion. Basal tear secretion is that under ordinary conditions with the eyelid open, and is considered being mainly from the accessory lacrimal glands e.g. Kraus gland and Wolfring gland. On the other hand, reflux tear secretion is tear secretion in response to some stimulation in the keratoconjunctival surface, nasal mucosa, or the like, or that accompanied with mental changes such as grief or joy. It is considered to be from the main lacrimal gland. Considering the symptoms of the dry-eye syndrome, improvement of the decreased basal tear secretion, i.e. tear secretion under ordinary conditions with the eyelid open, is particularly important.
Further, the diseases caused by external secretion disorders also include hyposalivation, and it may be sometimes accompanied by dry-mouth syndrome (xerostomia). In dry-mouth patients, the decreased amount of saliva secretion causes dryness of the lip and oral cavity and may induce thirst feeling, xerosis of tunica mucosa oris, urtication, dysmaesesis, and dyspepsia. Also, in the patients with dry-mouth syndrome, foods are likely to remain inside the mouth and may result in dental caries.
There are a variety of etiologic factors which are responsible for the dry-mouth syndrome. For example, systemic factors include febrile disease, dehydration, endocrinopathy (myxedema, Basedow's disease, diabetes insipidus, etc.) metabolic disorders (diabetes, uremia, liver cirrhosis, etc.) deficiency of Vitamin-A, B, autoimmune disease (Sjögren's syndrome, progressive scleroderma, etc.) anemia, bleeding, aging, various medicaments (sedatives, parasympatholytic drugs, antihistamines, etc.). Local factors include sialadenitis, atrophy of salivary gland, sequela of radio therapy, and malformation (ectodermal dysplasia, etc.)
As described above, there are a variety of known and unknown etiologic factors responsible for the dry-mouth syndrome. However, at present, only palliative treatments for the dry-mouth syndrome such as drinking liquid all day long little by little, chewing gum or the like, and using artificial saliva have been available. It has been desired to provide a composition which is capable of bringing fundamental treatment such that to improve the decreased saliva secretion.
Generally, a healthy normal person discharges 1 to 1.5 litter of saliva a day through a pair of left and right major salivary glands (including parotid gland, submandibular gland, and sublingual gland) and minor salivary glands (including labial glands, lingual glands, palatine glands, and buccal glands). Saliva is discharged in response to a stimulant which may harm body to dilute the same or to maintain the physiological pH value, as well as helping mastication and deglutition of foods. Further, saliva dissolves foods thereby makes a person taste them and helps him smoothly utter words by keeping a wet state inside the mouth. There are two types of saliva: one is the continuous type that keeps on discharging a small amount without a particular stimulant and the other is the reflective type that is discharged in response to stimulation by food, gnatho-movement, taste and the like. In any case, saliva secretion is one of the essential physiological functions and hence improving the decreased saliva secretion is particularly important in treating the dry-mouth syndrome.
In the past, some of fatty acids had been rated as essential, and enough amount of them were required to be taken from the nutrient point of view. Recently, bioactivities of a variety of fatty acids have been studied and the activities of linoleic acid, arachidonic acid, α-linolenic acid, eicosapentaenoic acid (EPA), and docosahexaenoic acid (DHA) have attracted the attention linoleic acid is converted through di-homo-γ-linolenic acid to arachidonic acid; α-linolenic acid is converted through eicosapentaenoic acid (EPA) to docosahexaenoic acid (DHA); di-homo-γ-linolenic acid is converted into type 1 prostaglandin (PG1), arachidonic acid is converted into type 2 prostaglandin (PG2) or type 4 leukotriene (LT4), and eicosapentaenoic acid is converted into type 3 prostaglandin or type 5 leukotriene (LT5) in vivo respectively.
Prostaglandins (hereinafter, referred to as PG(s)) are members of class of organic carboxylic acids, which are contained in tissues or organs of human or most other mammalian, and exhibit a wide range of physiological activity. PGs found in nature (primary PGs) generally have a prostanoic acid skeleton as shown in the formula (A):

On the other hand, some of synthetic analogues have a modified skeleton. The primary PGs are classified to PGAs, PGBs, PGCs, PGDs, PGES, PGFs, PGGs, PGHs, PGIs and PGJs according to the structure of the five-membered ring moiety, and further classified into the following three types by the number and position of the unsaturated bond at the carbon chain moiety:    subscript 1: 13,14-unsaturated-15-OH    subscript 2: 5,6- and 13,14-diunsaturated-15-OH    subscript 3: 5,6-, 13,14-, and 17,18-triunsaturated-15-OH.
Further, the PGFs are classified, according to the configuration of the hydroxyl group at the 9-position, into α type (the hydroxyl group is of an α-configuration) and β type (the hydroxyl group is of a β-configuration).
In addition, some 15-keto (i.e. having an oxo group at position 15 in place of the hydroxy group) prostaglandins and 13,14-dihydro-15-keto-prostaglandins are known as substances naturally produced by enzymatic actions during in vivo metabolism of primary PGs. 15-keto PGs have been disclosed in, for example, EP-A-0281239(corresponds to JP-A-104040/89), EP-A-0281480(corresponds to JP-A-52753/89), EP-A-0289349 (corresponds to JP-A-151552/89), EP-A-0453127(JP-A-58992/95) and EP-A-0690049(corresponds to JP-A-48665/96). These cited references are herein incorporated by reference.
For example, when a primary type PG such as PGE2 or PGF2α which is a fatty acid derivative is instilled to the eyes at a stimulating amount which induces conjunctival hyperemia, lacrimation will occur simultaneously with the hyperemia. However, at an amount as low as that does not induce any conjunctival hyperemia, it is not known about the effect of the fatty acid derivatives including PGs on the tear secretion, basal tear secretion which is not affected by a stimulant, nor saliva secretion.